Airbus A340 Series, Brochure

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STL 472.502/90 Issue 6
A340 Automatic Flight System - Autothrust Function
10.13
AP/FD and A/THR SPD/MACH modes
SPD/MACH managed mode :
• Is engaged by pushing the FCU SPD selector knob.
• AP/FD or A/THR holds the SPEED/MACH, as provided
by the FMS.
• Speed preset for next flight phase is available by
entering preset value on the MCDU; speed preset
becomes active at flight phase change.
• Crossover altitude is automatically provided.
SPD/MACH selected mode :
• Is engaged by pulling the FCU SPD selector knob.
• Crossover altitude is automatically provided.
• Manual SPD/MACH selection is available to the pilot
via the SPD/MACH conversion pushbutton.
AP/FD and A/THR SPD/MACH modes :
SPEED/MACH managed or selected may either be
controlled by AP/FD pitch mode or A/THR mode.
The reasons for this are as follows :
• An AP/FD pitch mode may control a flight path or
an indicated airspeed - but not both at the same
time.
• Thus, if the pitch mode (elevator) controls a flight
path, (G/S of V/S) the A/THR controls the IAS, but
if the pitch mode controls a speed (OPEN
CLB/OPEN DES), then the A/THR will control a
thrust.
Consequently, AP/FD pitch mode and A/THR are
linked so that, if no AP/FD is engaged, A/THR can
be active in SPD/MACH mode.